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References: <20231024201157.748254-1-alessandro.carminati@gmail.com> <20231026100732.f47cf41ef95a5c43915649b1@kernel.org>
In-Reply-To: <20231026100732.f47cf41ef95a5c43915649b1@kernel.org>
From:   Alessandro Carminati <alessandro.carminati@gmail.com>
Date:   Thu, 26 Oct 2023 18:08:47 +0200
Message-ID: <CAPp5cGQ+h3UdJ2b6JXoFDJcV5Bf64Pv4BmEHTbSJJd--Sq9jSw@mail.gmail.com>
Subject: Re: [PATCH v6] scripts/link-vmlinux.sh: Add alias to duplicate
 symbols for kallsyms
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Masahiro Yamada <masahiroy@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Daniel Bristot de Oliveira <bristot@kernel.org>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nicolas Schier <nicolas@fjasle.eu>,
        Alexander Lobakin <aleksander.lobakin@intel.com>,
        Nick Alcock <nick.alcock@oracle.com>,
        Kris Van Hees <kris.van.hees@oracle.com>,
        Eugene Loh <eugene.loh@oracle.com>,
        Francis Laniel <flaniel@linux.microsoft.com>,
        Viktor Malik <vmalik@redhat.com>,
        Petr Mladek <pmladek@suse.com>, Tom Rix <trix@redhat.com>,
        linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-trace-kernel@vger.kernel.org, llvm@lists.linux.dev
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Hello Masami,

Thank you for spending time to test this work.

Il giorno gio 26 ott 2023 alle ore 03:07 Masami Hiramatsu
<mhiramat@kernel.org> ha scritto:
>
> On Tue, 24 Oct 2023 20:11:57 +0000
> "Alessandro Carminati (Red Hat)" <alessandro.carminati@gmail.com> wrote:
>
> > In the kernel environment, scenarios often arise where identical names
> > are shared among symbols within core image or modules.
> > While this poses no complications for the kernel's binary itself, it
> > creates challenges when conducting trace or probe operations using tools
> > like kprobe.
> >
> > A solution has been introduced, referred to as "kas_alias."
> > During the kernel's build process, an extensive scan of all objects is
> > performed, encompassing both core kernel components and modules, to
> > collect comprehensive symbol information.
> > Subsequently, for all duplicate symbolsthe process enriches symbol names
> > by appending meaningful suffixes derived from source files and line
> > numbers.
> > These freshly generated aliases simplify interaction with symbols.
> >
> > The procedure is executed as follows.
> > During the kernel's build phase, an exhaustive search for duplicates among
> > symbols that share the same name in both kernel image and all modules
> > object files.
> > For the kernel core image, a new nem data file is created and alias for
> > all duplicate symbols is added.
> > For modules, the lib objects the ELF symtable is modified with the
> > addition of the alias for the duplicate symbols.
> >
> > Consider the symbol "device_show", you can expect an output like the
> > following:
> >
> >  ~ # cat /proc/kallsyms | grep " device_show"
> >  ffffffff963cd2a0 t device_show
> >  ffffffff963cd2a0 t device_show@drivers_pci_pci_sysfs_c_49
> >  ffffffff96454b60 t device_show
> >  ffffffff96454b60 t device_show@drivers_virtio_virtio_c_16
> >  ffffffff966e1700 T device_show_ulong
> >  ffffffff966e1740 T device_show_int
> >  ffffffff966e1770 T device_show_bool
> >  ffffffffc04e10a0 t device_show [mmc_core]
> >  ffffffffc04e10a0 t device_show@drivers_mmc_core_sdio_bus_c_45  [mmc_core]
> >
> > Signed-off-by: Alessandro Carminati (Red Hat) <alessandro.carminati@gmail.com>
> >
>
> Thanks for update. I tested that.
>
> Tested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>
> BTW, on my environment, the suffix path is not relative but absolute path
> (including /home/<user> etc.) I guess it is because I use O= option.
> This is another concerning point to fix.
Indeed, this point will be fixed in the next version.
Don't know why I assumed the build directory needed to be as a subdirectory
into the source tree.
>
>
> > NOTE1:
> > About the symbols name duplication that happens as consequence of the
> > inclusion compat_binfmt_elf.c does, it is evident that this corner is
> > inherently challenging the addr2line approach.
> > Attempting to conceal this limitation would be counterproductive.
> >
> > compat_binfmt_elf.c includes directly binfmt_elf.c, addr2line can't help
> > but report all functions and data declared by that file, coming from
> > binfmt_elf.c.
>
> Hmm, indeed. If we find such symbols we may need to add a suffix number
> to distinguish it, but it may confuse user that which symbol is for
> binfmt_elf or compat_binfmt_elf...
>
> >
> > My position is that, rather than producing a more complicated pipeline
> > to handle this corner case, it is better to fix the compat_binfmt_elf.c
> > anomaly.
>
> Agreed.
>
> >
> > This patch does not deal with the two potentially problematic symbols
> > defined by compat_binfmt_elf.c
>
> I think it is OK in this step.
>
> >
> > NOTE2:
> > The current implementation does not offer a solution for out-of-tree modules.
> > My stance is that these modules fall outside the scope, but I welcome any
> > comments or feedback regarding this matter.
>
> Can the out-of-tree developers run the kas_alias.py by themselves?
> Ah, we need to give them a table of all symbols (including other modules).
> If we do this in 2 phases, collect symbols, and inject aliases, then we can
> leave the tables of existing symbols as a file, and those out-of-tree module
> developers can reuse that file.
Yes, it can be done.
My idea would, rather than divide kas_alias into two scripts, to make it a
two actions script:
in_tree: to do the work kas_alias is already doing, and a new action,
out_of_tree: to add the new logic needed for out of tree modules.
As you suggested, the in_tree action will leave a file, I was thinking of
a JSON file, with the symbol frequencies, and the other action,
out_of_tree will use the file to produce the aliases.
>
>
> BTW, to hide the below changelogs (and above notes too?) from the commit,
> please put a '---' only line before that.
>
> Thank you!
>
> >
> > Changes from v1:
> > * Integrated changes requested by Masami to exclude symbols with prefixes
> >   "_cfi" and "_pfx".
> > * Introduced a small framework to handle patterns that need to be excluded
> >   from the alias production.
> > * Excluded other symbols using the framework.
> > * Introduced the ability to discriminate between text and data symbols.
> > * Added two new config symbols in this version:
> >   CONFIG_KALLSYMS_ALIAS_DATA, which allows data for data, and
> >   CONFIG_KALLSYMS_ALIAS_DATA_ALL, which excludes all filters and provides
> >   an alias for each duplicated symbol.
> >
> > https://lore.kernel.org/all/20230711151925.1092080-1-alessandro.carminati@gmail.com/
> >
> > Changes from v2:
> > * Alias tags are created by querying DWARF information from the vmlinux.
> > * The filename + line number is normalized and appended to the original
> >   name.
> > * The tag begins with '@' to indicate the symbol source.
> > * Not a change, but worth mentioning, since the alias is added to the
> >   existing list, the old duplicated name is preserved, and the livepatch
> >   way of dealing with duplicates is maintained.
> > * Acknowledging the existence of scenarios where inlined functions
> >   declared in header files may result in multiple copies due to compiler
> >   behavior, though it is not actionable as it does not pose an operational
> >   issue.
> > * Highlighting a single exception where the same name refers to different
> >   functions: the case of "compat_binfmt_elf.c," which directly includes
> >   "binfmt_elf.c" producing identical function copies in two separate
> >   modules.
> >
> > https://lore.kernel.org/all/20230714150326.1152359-1-alessandro.carminati@gmail.com/
> >
> > Changes from v3:
> > * kas_alias was rewritten in Python to create a more concise and
> >   maintainable codebase.
> > * The previous automation process used by kas_alias to locate the vmlinux
> >   and the addr2line has been replaced with an explicit command-line switch
> >   for specifying these requirements.
> > * addr2line has been added into the main Makefile.
> > * A new command-line switch has been introduced, enabling users to extend
> >   the alias to global data names.
> >
> > https://lore.kernel.org/all/20230828080423.3539686-1-alessandro.carminati@gmail.com/
> >
> > Changes from v4:
> > * Fixed the O=<build dir> build issue
> > * The tool halts execution upon encountering major issues, thereby ensuring
> >   the pipeline is interrupted.
> > * A cmdline option to specify the source directory added.
> > * Minor code adjusments.
> > * Tested on mips32 and i386
> >
> > https://lore.kernel.org/all/20230919193948.465340-1-alessandro.carminati@gmail.com/
> >
> > Changes from v5:
> > * Regex filter extended to all symbols
> > * Alias creation extended to module objects
> > * Code cleaned and commented
> > * kas_alias verbose execution via KAS_ALIAS_DEBUG env variable
> > * CONFIG_KALLSYMS_ALIAS_SRCLINE selects KBUILD_BUILTIN to ensure no races
> >   during modules build
> > * Tested on x86_64, aarch64 and i386
> >
> > https://lore.kernel.org/all/20230927173516.1456594-1-alessandro.carminati@gmail.com/
> > ---
> >  Makefile                  |  14 +-
> >  init/Kconfig              |  22 ++
> >  scripts/Makefile.modfinal |  10 +-
> >  scripts/kas_alias.py      | 545 ++++++++++++++++++++++++++++++++++++++
> >  scripts/link-vmlinux.sh   |  26 +-
> >  5 files changed, 613 insertions(+), 4 deletions(-)
> >  create mode 100755 scripts/kas_alias.py
> >
> > diff --git a/Makefile b/Makefile
> > index 4f283d915e54..f2c51340fa52 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -488,6 +488,7 @@ OBJCOPY           = $(LLVM_PREFIX)llvm-objcopy$(LLVM_SUFFIX)
> >  OBJDUMP              = $(LLVM_PREFIX)llvm-objdump$(LLVM_SUFFIX)
> >  READELF              = $(LLVM_PREFIX)llvm-readelf$(LLVM_SUFFIX)
> >  STRIP                = $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX)
> > +ADDR2LINE    = $(LLVM_PREFIX)llvm-addr2line$(LLVM_SUFFIX)
> >  else
> >  CC           = $(CROSS_COMPILE)gcc
> >  LD           = $(CROSS_COMPILE)ld
> > @@ -497,6 +498,7 @@ OBJCOPY           = $(CROSS_COMPILE)objcopy
> >  OBJDUMP              = $(CROSS_COMPILE)objdump
> >  READELF              = $(CROSS_COMPILE)readelf
> >  STRIP                = $(CROSS_COMPILE)strip
> > +ADDR2LINE    = $(CROSS_COMPILE)addr2line
> >  endif
> >  RUSTC                = rustc
> >  RUSTDOC              = rustdoc
> > @@ -611,7 +613,7 @@ export RUSTC_BOOTSTRAP := 1
> >  export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC HOSTPKG_CONFIG
> >  export RUSTC RUSTDOC RUSTFMT RUSTC_OR_CLIPPY_QUIET RUSTC_OR_CLIPPY BINDGEN CARGO
> >  export HOSTRUSTC KBUILD_HOSTRUSTFLAGS
> > -export CPP AR NM STRIP OBJCOPY OBJDUMP READELF PAHOLE RESOLVE_BTFIDS LEX YACC AWK INSTALLKERNEL
> > +export CPP AR NM STRIP OBJCOPY OBJDUMP READELF ADDR2LINE PAHOLE RESOLVE_BTFIDS LEX YACC AWK INSTALLKERNEL
> >  export PERL PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
> >  export KGZIP KBZIP2 KLZOP LZMA LZ4 XZ ZSTD
> >  export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE
> > @@ -1542,6 +1544,16 @@ KBUILD_BUILTIN := 1
> >  modules: vmlinux
> >  endif
> >
> > +# *.ko are usually independent of vmlinux, but CONFIG_KALLSYMS_ALIAS_SRCLINE
> > +# is another exception.
> > +# At the time when vmlinux is being linked, kas_alias operates on both vmlinux
> > +# and modules. To prevent races with modules, kas_alias needs to pause operations
> > +# while it is executed.
> > +ifdef CONFIG_KALLSYMS_ALIAS_SRCLINE
> > +KBUILD_BUILTIN := 1
> > +modules: vmlinux
> > +endif
> > +
> >  modules: modules_prepare
> >
> >  # Target to prepare building external modules
> > diff --git a/init/Kconfig b/init/Kconfig
> > index 6d35728b94b2..d45dd423e1ec 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -1738,6 +1738,28 @@ config KALLSYMS_BASE_RELATIVE
> >         time constants, and no relocation pass is required at runtime to fix
> >         up the entries based on the runtime load address of the kernel.
> >
> > +config KALLSYMS_ALIAS_SRCLINE
> > +     bool "Produces alias for duplicated text symbols" if EXPERT
> > +     depends on KALLSYMS && DEBUG_INFO && !DEBUG_INFO_SPLIT
> > +     help
> > +       It is not uncommon for drivers or modules related to similar
> > +       peripherals to have symbols with the exact same name.
> > +       While this is not a problem for the kernel's binary itself, it
> > +       becomes an issue when attempting to trace or probe specific
> > +       functions using infrastructure like ftrace or kprobe.
> > +
> > +       This option addresses this challenge, producing alias for text
> > +       symbol names that include the file name and line where the symbols
> > +       are defined in the source code.
> > +
> > +config KALLSYMS_ALIAS_SRCLINE_DATA
> > +     bool "Produces alias also for global variables names"
> > +     depends on KALLSYMS_ALIAS_SRCLINE
> > +     help
> > +       Sometimes it can be useful to refer to global vars by name. Since
> > +       they suffer the same issue as text symbols, this config option
> > +       allows having aliases for global variables names too.
> > +
> >  # end of the "standard kernel features (expert users)" menu
> >
> >  # syscall, maps, verifier
> > diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> > index b3a6aa8fbe8c..3d9756a6eb3e 100644
> > --- a/scripts/Makefile.modfinal
> > +++ b/scripts/Makefile.modfinal
> > @@ -15,6 +15,14 @@ include $(srctree)/scripts/Makefile.lib
> >  # find all modules listed in modules.order
> >  modules := $(call read-file, $(MODORDER))
> >
> > +ifeq ($(KBUILD_BUILTIN),y)
> > +  ifeq ($(or $(CONFIG_DEBUG_INFO_BTF_MODULES),$(CONFIG_KALLSYMS_ALIAS_SRCLINE)),y)
> > +    VMLINUX_DEP := vmlinux
> > +  endif
> > +endif
> > +
> > +VMLINUX_DEP ?=
> > +
> >  __modfinal: $(modules:%.o=%.ko)
> >       @:
> >
> > @@ -55,7 +63,7 @@ if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check),      \
> >       printf '%s\n' 'savedcmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
> >
> >  # Re-generate module BTFs if either module's .ko or vmlinux changed
> > -%.ko: %.o %.mod.o scripts/module.lds $(and $(CONFIG_DEBUG_INFO_BTF_MODULES),$(KBUILD_BUILTIN),vmlinux) FORCE
> > +%.ko: %.o %.mod.o scripts/module.lds $(VMLINUX_DEP) FORCE
> >       +$(call if_changed_except,ld_ko_o,vmlinux)
> >  ifdef CONFIG_DEBUG_INFO_BTF_MODULES
> >       +$(if $(newer-prereqs),$(call cmd,btf_ko))
> > diff --git a/scripts/kas_alias.py b/scripts/kas_alias.py
> > new file mode 100755
> > index 000000000000..bc930039867b
> > --- /dev/null
> > +++ b/scripts/kas_alias.py
> > @@ -0,0 +1,545 @@
> > +#!/usr/bin/env python3
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +#
> > +# Copyright (C) 2023 Red Hat, Inc. Alessandro Carminati <alessandro.carminati@gmail.com>
> > +#
> > +# kas_alias: Adds alias to duplicate symbols for the kallsyms output.
> > +
> > +import os
> > +import re
> > +import argparse
> > +import subprocess
> > +from enum import Enum
> > +from collections import namedtuple
> > +
> > +# Regex representing symbols that needs no alias
> > +regex_filter = [
> > +        "^__compound_literal\\.[0-9]+$",
> > +        "^__[wm]*key\\.[0-9]+$",
> > +        "^_*TRACE_SYSTEM.*$",
> > +        "^__already_done\\.[0-9]+$",
> > +        "^__msg\\.[0-9]+$",
> > +        "^__func__\\.[0-9]+$",
> > +        "^CSWTCH\\.[0-9]+$",
> > +        "^_rs\\.[0-9]+$",
> > +        "^___tp_str\\.[0-9]+$",
> > +        "^__flags\\.[0-9]+$",
> > +        "^___done\\.[0-9]+$",
> > +        "^__print_once\\.[0-9]+$",
> > +        "^___once_key\\.[0-9]+$",
> > +        "^__pfx_.*$",
> > +        "^__cfi_.*$",
> > +        "^\\.LC[0-9]+$",
> > +        "^\\.L[0-9]+.[0-9]+$",
> > +        "^__UNIQUE_ID_.*$",
> > +        "^symbols\\.[0-9]+$",
> > +        "^_note_[0-9]+$"
> > +        ]
> > +
> > +class DebugLevel(Enum):
> > +    PRODUCTION = 0
> > +    INFO = 1
> > +    DEBUG_BASIC = 2
> > +    DEBUG_MODULES = 3
> > +    DEBUG_ALL = 4
> > +
> > +class SeparatorType:
> > +    def __call__(self, separator):
> > +        if len(separator) != 1:
> > +            raise argparse.ArgumentTypeError("Separator must be a single character")
> > +        return separator
> > +
> > +class Addr2LineError(Exception):
> > +    pass
> > +
> > +debug = DebugLevel.PRODUCTION
> > +
> > +Line = namedtuple('Line', ['address', 'type', 'name'])
> > +
> > +def parse_nm_lines(lines, name_occurrences=None):
> > +    """
> > +    Parses a given nm output and returns the symbol list along with a hash of
> > +    symbol occurrences.
> > +    Args:
> > +      lines: List of tuples representing one nm line.
> > +      name_occurrences: Hash having the name as key, used to count names'
> > +                        occurrences.
> > +    Returns:
> > +      Creates a new line list proper for the nm output it parsed and, updates
> > +      the occurrences hash.
> > +  """
> > +    if debug >= DebugLevel.DEBUG_BASIC.value:
> > +       print("parse_nm_lines: parse start")
> > +
> > +    if name_occurrences is None:
> > +        name_occurrences = {}
> > +
> > +    symbol_list = []
> > +
> > +    for line in lines:
> > +        fields = line.strip().split()
> > +
> > +        if len(fields) >= 3:
> > +            address, type, name = fields[0], fields[1], ' '.join(fields[2:])
> > +            symbol_list.append(Line(address, type, name))
> > +            name_occurrences[name] = name_occurrences.get(name, 0) + 1
> > +
> > +    return symbol_list, name_occurrences
> > +
> > +def start_addr2line_process(binary_file, addr2line_file):
> > +    """
> > +    Initializes an addr2line server process operating on the given ELF object.
> > +    Args:
> > +      binary_file: String representing the binary file name object of addr2line
> > +                   queries.
> > +      addr2line_file: String representing the addr2line executable name.
> > +    Returns:
> > +      Returns addr2line process descriptor.
> > +    """
> > +    if debug >= DebugLevel.DEBUG_BASIC.value:
> > +       print(f"start_addr2line_process: Starting addr2line process on {binary_file}")
> > +
> > +    try:
> > +        addr2line_process = subprocess.Popen([addr2line_file, '-fe',
> > +                                             binary_file],
> > +                                             stdin=subprocess.PIPE,
> > +                                             stdout=subprocess.PIPE,
> > +                                             stderr=subprocess.PIPE,
> > +                                             text=True)
> > +        return addr2line_process
> > +    except Exception as e:
> > +         raise SystemExit(f"Fatal: Can't start addr2line resolver: {e}")
> > +
> > +
> > +def addr2line_fetch_address(addr2line_process, address):
> > +    """
> > +    Queries a specific address using the active addr2line process.
> > +    Args:
> > +      addr2line_process: Descriptor of the addr2line process that is wanted to
> > +                         handle the query.
> > +      address: The address of the symbol that needs to be resolved.
> > +    Returns:
> > +      Returns a string representing the file and line number where the symbol
> > +      at the specified address has been defined. The address is normalized
> > +      before being returned.
> > +  """
> > +    if debug >= DebugLevel.DEBUG_ALL.value:
> > +       print(f"addr2line_fetch_address: Resolving {address}")
> > +
> > +    try:
> > +        addr2line_process.stdin.write(address + '\n')
> > +        addr2line_process.stdin.flush()
> > +        addr2line_process.stdout.readline().strip()
> > +        output = addr2line_process.stdout.readline().strip()
> > +
> > +        return os.path.normpath(output)
> > +    except Exception as e:
> > +        raise SystemExit(
> > +                         "Fatal: Error communicating with"
> > +                         f" the addr2line resolver: {e}."
> > +                        )
> > +
> > +def process_line(line, process_data_sym, init_section_info):
> > +    """
> > +    Determines whether a duplicate item requires an alias or not.
> > +    Args:
> > +      line: nm line object that needs to be checked.
> > +      process_data_sym: Flag indicating that the script requires to produce alias
> > +                        also for data symbols.
> > +    Returns:
> > +      Returns true if the line needs to be processed, false otherwise.
> > +    """
> > +    if debug >= DebugLevel.DEBUG_ALL.value:
> > +       print(f"process_line: Processing {line.address} {line.type} {line.name}")
> > +
> > +    # The module contains symbols that were discarded after being loaded. Typically,
> > +    # these symbols belong to the initialization function. These symbols have their
> > +    # address in the init section addresses, so this check prevents these symbols
> > +    # from being assigned aliases.
> > +    if init_section_info != None:
> > +        if (int(line.address, 16) >= init_section_info["address"] and
> > +          int(line.address, 16) <= init_section_info["address"] + init_section_info["size"]):
> > +            if debug >= DebugLevel.DEBUG_ALL.value:
> > +                print(f"process_line: Skip {line.name} since its address is .init.text")
> > +            return False
> > +
> > +    if process_data_sym:
> > +        return not (any(re.match(regex, line.name) for regex in regex_filter))
> > +    else:
> > +        return (line.type in {"T", "t"}) and (
> > +                not (any(re.match(regex, line.name) for regex in regex_filter)))
> > +
> > +def fetch_file_lines(filename):
> > +    """
> > +    Reads a text file and retrieves its content.
> > +    Args:
> > +      filename: String representing the name of the file that needs to be read.
> > +    Returns:
> > +      Returns a string list representing the lines read in the file.
> > +    """
> > +    if debug >= DebugLevel.DEBUG_BASIC.value:
> > +       print(f"fetch_file_lines: Fetch {filename}")
> > +
> > +    try:
> > +        with open(filename, 'r') as file:
> > +            lines = [line.strip() for line in file.readlines()]
> > +        return lines
> > +    except FileNotFoundError:
> > +        raise SystemExit(f"Fatal: File not found: {filename}")
> > +
> > +def do_nm(filename, nm_executable):
> > +    """
> > +    Runs the nm command on a specified file.
> > +    Args:
> > +      filename: String representing the name of the file on which nm should
> > +      run against.
> > +      nm_executable: String representing the nm executable filename.
> > +    Returns:
> > +      Returns a strings list representing the nm output.
> > +    """
> > +    # Later, during processing, objcopy cannot modify files in place when
> > +    # adding new alias symbols. It requires a source file and a destination
> > +    # file.
> > +    # After this operation, there is an object file ".o" with the aliases and
> > +    # a ".k{0,1}o.orig" file, which is the old intended object and serves as the
> > +    # source for objcopy.
> > +    # In a fresh build, the state is just fine.
> > +    # However, in a second build without clean, an issue arises.
> > +    # The ".k{0,1}o" file already contain the alias, and reprocessing it, do
> > +    # corrupt the final result. To address this, do_nm must check if the file
> > +    # ".k{0,1}o.orig" already exists.
> > +    # If it does, that's the target for nm and must be renamed in ".k{0,1}o"
> > +    # to restore the intended state. If not, it's a fresh build, and nm can
> > +    # proceed with the ".k{0,1}o" file.
> > +    backup_file = filename + '.orig'
> > +    if os.path.exists(backup_file):
> > +        print(f"do_nm: {filename} is not clean, restore {backup_file} to {filename}")
> > +        os.rename(backup_file, filename)
> > +
> > +    if debug >= DebugLevel.DEBUG_BASIC.value:
> > +       print(f"do_nm: executing {nm_executable} -n {filename}")
> > +
> > +    try:
> > +        nm_output = subprocess.check_output([nm_executable, '-n', filename],
> > +                      universal_newlines=True, stderr=subprocess.STDOUT).splitlines()
> > +        return nm_output
> > +    except subprocess.CalledProcessError as e:
> > +        raise SystemExit(f"Fatal: Error executing nm: {e}")
> > +
> > +def make_objcpy_arg(line, decoration, elf_section_names):
> > +    """
> > +    Produces an objcopy argument statement for a single alias to be added in a
> > +    module.
> > +    Args:
> > +      line: nm line object target for this iteration.
> > +      decoration: String representing the decoration (normalized addr2line
> > +                  output) to be added at the symbol name to have the alias.
> > +      elf_section_names: List of the section names that can be used by objcopy
> > +                         to add a symbol to the ELF symbol table.
> > +    Returns:
> > +      Returns a string that directly maps the argument string objcopy should
> > +      use to add the alias.
> > +    """
> > +    try:
> > +        section = (
> > +            elf_section_names[".text"] if line.type.upper() == "T" else (
> > +                elf_section_names[".data"] if line.type.upper() == "D" else (
> > +                    elf_section_names[".rodata"] if line.type.upper() == "R" else ".bss"
> > +                )
> > +            )
> > +        )
> > +        flag = "global" if line.type.isupper() else "local"
> > +
> > +        if debug >= DebugLevel.DEBUG_MODULES.value:
> > +           print("make_objcpy_arg: "
> > +                 f"{line.name + decoration}={section}:0x{line.address},{flag}")
> > +
> > +
> > +        return (
> > +                "--add-symbol "
> > +                f"{line.name + decoration}={section}:0x{line.address},{flag} "
> > +               )
> > +    except Exception:
> > +        print(
> > +              f"make_objcpy_arg warning: Skip alias for {line.name}"
> > +              f" type {line.type} because no corresponding section found.")
> > +        return ""
> > +
> > +def execute_objcopy(objcopy_executable, objcopy_args, object_file):
> > +    """
> > +    Uses objcopy to add aliases to a given module object file.
> > +    Since objcopy can't operate in place, the original object file is renamed
> > +    before operating on it. At function end, a new object file having the old
> > +    object's name is carrying the aliases for the duplicate symbols.
> > +    Args:
> > +      objcopy_executable: String representing the object copy executable file.
> > +      objcopy_args: Arguments (aliases to add to the object file) to be used
> > +                    in the objcopy execution command line.
> > +      object_file: Target object file (module object file) against which objcopy is executed.
> > +    Returns:
> > +      Nothing is returned, but as a side effect of this function execution,
> > +      the module's object file contains the aliases for duplicated symbols.
> > +    """
> > +    # Rename the original object file by adding a suffix
> > +    backup_file = object_file + '.orig'
> > +    if debug >= DebugLevel.DEBUG_MODULES.value:
> > +       print("execute_objcopy: "
> > +             f"rename {object_file} to {backup_file}")
> > +    os.rename(object_file, backup_file)
> > +
> > +    full_command = (
> > +                    f"{objcopy_executable} "
> > +                    f"{objcopy_args} {backup_file} {object_file}"
> > +                   )
> > +    if debug >= DebugLevel.DEBUG_MODULES.value:
> > +       print(f"execute_objcopy: executing {full_command}")
> > +
> > +    try:
> > +        subprocess.run(full_command, shell=True, check=True)
> > +    except subprocess.CalledProcessError as e:
> > +        os.rename(backup_file, object_file)
> > +        raise SystemExit(f"Fatal: Error executing objcopy: {e}")
> > +
> > +def generate_decoration(line, config, addr2line_process):
> > +    """
> > +    Generates symbol decoration to be used to make the alias name, by
> > +    querying addr2line.
> > +    Args:
> > +      line: nm line object that needs an alias.
> > +      config: Object containing command line configuration.
> > +      addr2line_process: Descriptor of the addr2line process that serves
> > +                         the binary object where the symbol belongs.
> > +    Returns:
> > +      Returns a string representing the decoration for the given symbol,
> > +      or empty string if this can not be done. E.g., addr2line can't find
> > +      the point where the symbol is defined.
> > +    """
> > +    output = addr2line_fetch_address(addr2line_process, line.address)
> > +    decoration = config.separator + "".join(
> > +        "_" if not c.isalnum() else c for c in output.replace(config.linux_base_dir, "")
> > +    )
> > +    # The addr2line can emit the special string "?:??" when addr2line can not find the
> > +    # specified address in the DWARF section that after normalization it becomes "____".
> > +    # In such cases, emitting an alias wouldn't make sense, so it is skipped.
> > +    if decoration != config.separator + "____":
> > +       return decoration
> > +    return ""
> > +
> > +def get_objdump_text(objdump_executable, file_to_operate):
> > +    """
> > +    objdump output is needed for a couple of functions revolving around
> > +    modules. This function kust query objdump to emit sections info and
> > +    return its output.
> > +    Args:
> > +      objdump_executable: String representing the objdump executable.
> > +      file_to_operate: file whose section names are wanted.
> > +    Returns:
> > +      Returns objdump output.
> > +    """
> > +    try:
> > +        output = subprocess.check_output(
> > +                   [objdump_executable, '-h', file_to_operate],
> > +                   universal_newlines=True)
> > +
> > +    except Exception as e:
> > +        raise SystemExit(
> > +                         "Fatal: Can't find section names"
> > +                         f" for {file_to_operate}. Error: {e}"
> > +                        )
> > +    return output
> > +
> > +def get_init_text_info(objdump_lines):
> > +    """
> > +    Recovers info on the .init.text section.
> > +    Args:
> > +      objdump_lines: output from objdump -h command.
> > +    Returns:
> > +      Returns a map containing the size and address of the .init.text section
> > +      None if it is not there.
> > +    """
> > +    section_info = None
> > +    section_name_pattern = re.compile(r'^\s*\d+')
> > +
> > +    for line in objdump_lines.strip().splitlines():
> > +        if section_name_pattern.match(line):
> > +            parts = line.split()
> > +            if len(parts) >= 2:
> > +                current_section_name = parts[1]
> > +                if current_section_name == ".init.text":
> > +                    size = int(parts[2], 16)
> > +                    address = int(parts[3], 16)
> > +                    section_info = {"size": size, "address": address}
> > +                    break
> > +
> > +    return section_info
> > +
> > +def get_section_names(objdump_lines):
> > +    """
> > +    objcopy needs to refer to a section name to assign the symbol type.
> > +    Unfortunately, not always all the section are present into a given
> > +    object file exist, for example, ".rodata" can not exist, and a [Rr]
> > +    symbol my refer to some other section e.g., ".rodata.str1".
> > +    For this reason this function tries to recover the exact names to use
> > +    in an objcopy statement.
> > +    Args:
> > +      objdump_lines: output from objdump -h command.
> > +    Returns:
> > +      Returns a map containing four string indexed with typical section
> > +      names.
> > +    """
> > +    section_names = []
> > +    lines = objdump_lines.strip().splitlines()
> > +    section_name_pattern = re.compile(r'^\s*\d+')
> > +    for line in lines:
> > +        if section_name_pattern.match(line):
> > +            parts = line.split()
> > +            if len(parts) >= 2:
> > +                section_name = parts[1]
> > +                section_names.append(section_name)
> > +
> > +    best_matches = [".text", ".rodata", ".data", ".bss"]
> > +    result = {}
> > +
> > +    for match in best_matches:
> > +        for section_name in section_names:
> > +            if re.match(match+".*", section_name):
> > +                result[match] = section_name
> > +
> > +    if debug >= DebugLevel.DEBUG_MODULES.value:
> > +        for key, value in result.items():
> > +            print(f"get_section_names: sections {key} = {value}")
> > +
> > +    return result
> > +
> > +def produce_output_modules(config, symbol_list, name_occurrences,
> > +                           module_file_name, addr2line_process):
> > +    """
> > +    Computes the alias addition on a given module object file.
> > +    Args:
> > +      config: Object containing command line configuration.
> > +      symbol_list: List of tuples representing nm lines for the given object
> > +                   file.
> > +      name_occurrences: Hash that stores symbol occurreces for the build.
> > +      module_file_name: String representing the target moule object file.
> > +      addr2line_process: Descriptor of the addr2line process that is wanted to
> > +                         handle the query.
> > +    Returns:
> > +      Nothing is returned, but as a side effect of this function execution,
> > +      the module's object file contains the aliases for duplicated symbols.
> > +    """
> > +    objcopy_args = "";
> > +    args_cnt = 0
> > +    objdump_data = get_objdump_text(config.objdump_file, module_file_name)
> > +    elf_section_names = get_section_names(objdump_data)
> > +    init_text_section_data = get_init_text_info(objdump_data)
> > +    for obj in symbol_list:
> > +        if (name_occurrences[obj.name] > 1) and process_line(obj, config.process_data_sym, init_text_section_data):
> > +            decoration = generate_decoration(obj, config, addr2line_process)
> > +            if decoration != "":
> > +                objcopy_args = objcopy_args + make_objcpy_arg(obj, decoration, elf_section_names)
> > +                args_cnt = args_cnt + 1
> > +                if args_cnt > 50:
> > +                   if debug >= DebugLevel.DEBUG_MODULES.value:
> > +                      print("Produce_output_modules: Number of arguments high, split objcopy call into multiple statements.")
> > +                   execute_objcopy(config.objcopy_file, objcopy_args, module_file_name)
> > +                   args_cnt = 0
> > +                   objcopy_args = ""
> > +
> > +    execute_objcopy(config.objcopy_file, objcopy_args, module_file_name)
> > +
> > +def produce_output_vmlinux(config, symbol_list, name_occurrences, addr2line_process):
> > +    """
> > +    Computes the alias addition for the core Linux on image.
> > +    Args:
> > +      config: Object containing command line configuration.
> > +      symbol_list: List of tuples representing nm lines for the given object
> > +                   file.
> > +      name_occurrences: Hash that stores symbol occurreces for the build.
> > +      addr2line_process: Descriptor of the addr2line process that is wanted to
> > +                         handle the query.
> > +    Returns:
> > +      Nothing is returned, but as a side effect of this function execution,
> > +      the core kernel image contains the aliases for duplicated symbols.
> > +    """
> > +    with open(config.output_file, 'w') as output_file:
> > +        for obj in symbol_list:
> > +            output_file.write(f"{obj.address} {obj.type} {obj.name}\n")
> > +            if (name_occurrences[obj.name] > 1) and process_line(obj, config.process_data_sym, None):
> > +                decoration = generate_decoration(obj, config, addr2line_process)
> > +                if decoration != "":
> > +                    output_file.write(f"{obj.address} {obj.type} {obj.name + decoration}\n")
> > +
> > +if __name__ == "__main__":
> > +    # Handles command-line arguments and generates a config object
> > +    parser = argparse.ArgumentParser(description='Add alias to multiple occurring symbols name in kallsyms')
> > +    parser.add_argument('-a', "--addr2line", dest="addr2line_file", required=True, help="Set the addr2line executable to be used.")
> > +    parser.add_argument('-b', "--basedir", dest="linux_base_dir", required=True, help="Set base directory of the source kernel code.")
> > +    parser.add_argument('-c', "--objcopy", dest="objcopy_file", required=True, help="Set the objcopy executable to be used.")
> > +    parser.add_argument('-d', "--process_data", dest="process_data_sym", required=False, help="Requires the tool to process data symbols along with text symbols.", action='store_true')
> > +    parser.add_argument('-e', "--nm", dest="nm_file", required=True, help="Set the nm executable to be used.")
> > +    parser.add_argument('-m', "--modules_list", dest="module_list", required=True, help="Set the file containing the list of the modules object files.")
> > +    parser.add_argument('-n', "--nmdata", dest="nm_data_file", required=True, help="Set vmlinux nm output file to use for core image.")
> > +    parser.add_argument('-o', "--outfile", dest="output_file", required=True, help="Set the vmlinux nm output file containing aliases.")
> > +    parser.add_argument('-s', "--separator", dest="separator", required=False, help="Set separator, character that separates original name from the addr2line data in alias symbols.", default="@", type=SeparatorType())
> > +    parser.add_argument('-u', "--objdump", dest="objdump_file", required=True, help="Set objdump  executable to be used.")
> > +    parser.add_argument('-v', "--vmlinux", dest="vmlinux_file", required=True, help="Set the vmlinux core image file.")
> > +    parser.add_argument('-z', "--debug", dest="debug", required=False, help="Set the debug level.", choices=[f"{level.value}" for level in DebugLevel], default="1" )
> > +    config = parser.parse_args()
> > +    debug = int(config.debug)
> > +
> > +    try:
> > +        if debug >= DebugLevel.INFO.value:
> > +            print("kas_alias: Start processing")
> > +
> > +        # Determine kernel source code base directory
> > +        config.linux_base_dir = os.path.normpath(os.getcwd() + "/" + config.linux_base_dir) + "/"
> > +
> > +        if debug >= DebugLevel.INFO.value:
> > +            print("kas_alias: Process nm data from vmlinux")
> > +
> > +        # Process nm data from vmlinux
> > +        vmlinux_nm_lines = fetch_file_lines(config.nm_data_file)
> > +        vmlinux_symbol_list, name_occurrences = parse_nm_lines(vmlinux_nm_lines)
> > +
> > +        if debug >= DebugLevel.INFO.value:
> > +            print("kas_alias: Process nm data for modules")
> > +
> > +        # Process nm data for modules
> > +        module_list = fetch_file_lines(config.module_list)
> > +        module_symbol_list = {}
> > +        for module in module_list:
> > +            module_nm_lines = do_nm(module, config.nm_file)
> > +            module_symbol_list[module], name_occurrences = parse_nm_lines(module_nm_lines, name_occurrences)
> > +
> > +        if debug >= DebugLevel.INFO.value:
> > +            print("kas_alias: Produce file for vmlinux")
> > +
> > +        # Produce file for vmlinux
> > +        addr2line_process = start_addr2line_process(config.vmlinux_file, config.addr2line_file)
> > +        produce_output_vmlinux(config, vmlinux_symbol_list, name_occurrences, addr2line_process)
> > +        addr2line_process.stdin.close()
> > +        addr2line_process.stdout.close()
> > +        addr2line_process.stderr.close()
> > +        addr2line_process.wait()
> > +
> > +        # link-vmlinux.sh calls this two times: Avoid running kas_alias twice for efficiency and prevent duplicate aliases
> > +        # in module processing by checking the last letter of the nm data file
> > +        if config.vmlinux_file and config.vmlinux_file[-1] == '2':
> > +            if debug >= DebugLevel.INFO.value:
> > +                print("kas_alias: Add aliases to module files")
> > +
> > +            # Add aliases to module files
> > +            for module in module_list:
> > +                addr2line_process = start_addr2line_process(module, config.addr2line_file)
> > +                produce_output_modules(config, module_symbol_list[module], name_occurrences, module, addr2line_process)
> > +                addr2line_process.stdin.close()
> > +                addr2line_process.stdout.close()
> > +                addr2line_process.stderr.close()
> > +                addr2line_process.wait()
> > +        else:
> > +            if debug >= DebugLevel.INFO.value:
> > +                print("kas_alias: Skip module processing if pass is not the second")
> > +
> > +
> > +    except Exception as e:
> > +        raise SystemExit(f"Script terminated due to an error: {e}")
> > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> > index a432b171be82..beb94f1f7961 100755
> > --- a/scripts/link-vmlinux.sh
> > +++ b/scripts/link-vmlinux.sh
> > @@ -91,7 +91,12 @@ vmlinux_link()
> >
> >       # The kallsyms linking does not need debug symbols included.
> >       if [ "$output" != "${output#.tmp_vmlinux.kallsyms}" ] ; then
> > -             ldflags="${ldflags} ${wl}--strip-debug"
> > +             # The kallsyms linking does not need debug symbols included,
> > +             # unless the KALLSYMS_ALIAS_SRCLINE.
> > +             if ! is_enabled CONFIG_KALLSYMS_ALIAS_SRCLINE && \
> > +                [ "$output" != "${output#.tmp_vmlinux.kallsyms}" ] ; then
> > +                     ldflags="${ldflags} ${wl}--strip-debug"
> > +             fi
> >       fi
> >
> >       if is_enabled CONFIG_VMLINUX_MAP; then
> > @@ -161,7 +166,23 @@ kallsyms()
> >       fi
> >
> >       info KSYMS ${2}
> > -     scripts/kallsyms ${kallsymopt} ${1} > ${2}
> > +     ALIAS=""
> > +     KAS_DATA=""
> > +     if is_enabled CONFIG_KALLSYMS_ALIAS_SRCLINE_DATA; then
> > +             KAS_DATA="--process_data"
> > +     fi
> > +     if is_enabled CONFIG_KALLSYMS_ALIAS_SRCLINE; then
> > +             ALIAS=".alias"
> > +             # You can use KAS_ALIAS_DEBUG=<debug level> in the make statements to enable
> > +             # verbose execution for kas_alias.
> > +             ${srctree}/scripts/kas_alias.py \
> > +                     --addr2line ${ADDR2LINE} --vmlinux ${kallsyms_vmlinux} \
> > +                     --nmdata ${1} --outfile ${1}${ALIAS} \
> > +                     --modules_list ${MODORDER} --nm ${NM} --debug ${KAS_ALIAS_DEBUG:-0}\
> > +                     --objdump ${OBJDUMP} --objcopy ${OBJCOPY} \
> > +                     --basedir ${srctree} --separator @ ${KAS_DATA}
> > +     fi
> > +     scripts/kallsyms ${kallsymopt} ${1}${ALIAS} > ${2}
> >  }
> >
> >  # Perform one step in kallsyms generation, including temporary linking of
> > @@ -203,6 +224,7 @@ cleanup()
> >       rm -f System.map
> >       rm -f vmlinux
> >       rm -f vmlinux.map
> > +     find . -type f -name "*.orig" -exec rm {} \;
> >  }
> >
> >  # Use "make V=1" to debug this script
> > --
> > 2.34.1
> >
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>
Regards
Alessandro